datafusion_functions/unicode/
substr.rs

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

use std::any::Any;
use std::cmp::max;
use std::sync::Arc;

use crate::utils::{make_scalar_function, utf8_to_str_type};
use arrow::array::{
    make_view, Array, ArrayAccessor, ArrayIter, ArrayRef, AsArray, ByteView,
    GenericStringArray, OffsetSizeTrait, StringViewArray,
};
use arrow::datatypes::DataType;
use arrow_buffer::{NullBufferBuilder, ScalarBuffer};
use datafusion_common::cast::as_int64_array;
use datafusion_common::{exec_datafusion_err, exec_err, Result};
use datafusion_expr::TypeSignature::Exact;
use datafusion_expr::{ColumnarValue, ScalarUDFImpl, Signature, Volatility};

#[derive(Debug)]
pub struct SubstrFunc {
    signature: Signature,
    aliases: Vec<String>,
}

impl Default for SubstrFunc {
    fn default() -> Self {
        Self::new()
    }
}

impl SubstrFunc {
    pub fn new() -> Self {
        use DataType::*;
        Self {
            signature: Signature::one_of(
                vec![
                    Exact(vec![Utf8, Int64]),
                    Exact(vec![LargeUtf8, Int64]),
                    Exact(vec![Utf8, Int64, Int64]),
                    Exact(vec![LargeUtf8, Int64, Int64]),
                    Exact(vec![Utf8View, Int64]),
                    Exact(vec![Utf8View, Int64, Int64]),
                ],
                Volatility::Immutable,
            ),
            aliases: vec![String::from("substring")],
        }
    }
}

impl ScalarUDFImpl for SubstrFunc {
    fn as_any(&self) -> &dyn Any {
        self
    }

    fn name(&self) -> &str {
        "substr"
    }

    fn signature(&self) -> &Signature {
        &self.signature
    }

    fn return_type(&self, arg_types: &[DataType]) -> Result<DataType> {
        if arg_types[0] == DataType::Utf8View {
            Ok(DataType::Utf8View)
        } else {
            utf8_to_str_type(&arg_types[0], "substr")
        }
    }

    fn invoke(&self, args: &[ColumnarValue]) -> Result<ColumnarValue> {
        make_scalar_function(substr, vec![])(args)
    }

    fn aliases(&self) -> &[String] {
        &self.aliases
    }
}

/// Extracts the substring of string starting at the start'th character, and extending for count characters if that is specified. (Same as substring(string from start for count).)
/// substr('alphabet', 3) = 'phabet'
/// substr('alphabet', 3, 2) = 'ph'
/// The implementation uses UTF-8 code points as characters
pub fn substr(args: &[ArrayRef]) -> Result<ArrayRef> {
    match args[0].data_type() {
        DataType::Utf8 => {
            let string_array = args[0].as_string::<i32>();
            string_substr::<_, i32>(string_array, &args[1..])
        }
        DataType::LargeUtf8 => {
            let string_array = args[0].as_string::<i64>();
            string_substr::<_, i64>(string_array, &args[1..])
        }
        DataType::Utf8View => {
            let string_array = args[0].as_string_view();
            string_view_substr(string_array, &args[1..])
        }
        other => exec_err!(
            "Unsupported data type {other:?} for function substr,\
            expected Utf8View, Utf8 or LargeUtf8."
        ),
    }
}

// Convert the given `start` and `count` to valid byte indices within `input` string
// Input `start` and `count` are equivalent to PostgreSQL's `substr(s, start, count)`
// `start` is 1-based, if `count` is not provided count to the end of the string
// Input indices are character-based, and return values are byte indices
// The input bounds can be outside string bounds, this function will return
// the intersection between input bounds and valid string bounds
//
// * Example
// 'Hi🌏' in-mem (`[]` for one char, `x` for one byte): [x][x][xxxx]
// `get_true_start_end('Hi🌏', 1, None) -> (0, 6)`
// `get_true_start_end('Hi🌏', 1, 1) -> (0, 1)`
// `get_true_start_end('Hi🌏', -10, 2) -> (0, 0)`
fn get_true_start_end(input: &str, start: i64, count: Option<u64>) -> (usize, usize) {
    let start = start - 1;
    let end = match count {
        Some(count) => start + count as i64,
        None => input.len() as i64,
    };
    let count_to_end = count.is_some();

    let start = start.clamp(0, input.len() as i64) as usize;
    let end = end.clamp(0, input.len() as i64) as usize;
    let count = end - start;

    let (mut st, mut ed) = (input.len(), input.len());
    let mut start_counting = false;
    let mut cnt = 0;
    for (char_cnt, (byte_cnt, _)) in input.char_indices().enumerate() {
        if char_cnt == start {
            st = byte_cnt;
            if count_to_end {
                start_counting = true;
            } else {
                break;
            }
        }
        if start_counting {
            if cnt == count {
                ed = byte_cnt;
                break;
            }
            cnt += 1;
        }
    }
    (st, ed)
}

/// Make a `u128` based on the given substr, start(offset to view.offset), and
/// push into to the given buffers
fn make_and_append_view(
    views_buffer: &mut Vec<u128>,
    null_builder: &mut NullBufferBuilder,
    raw: &u128,
    substr: &str,
    start: u32,
) {
    let substr_len = substr.len();
    let sub_view = if substr_len > 12 {
        let view = ByteView::from(*raw);
        make_view(substr.as_bytes(), view.buffer_index, view.offset + start)
    } else {
        // inline value does not need block id or offset
        make_view(substr.as_bytes(), 0, 0)
    };
    views_buffer.push(sub_view);
    null_builder.append_non_null();
}

// The decoding process refs the trait at: arrow/arrow-data/src/byte_view.rs:44
// From<u128> for ByteView
fn string_view_substr(
    string_view_array: &StringViewArray,
    args: &[ArrayRef],
) -> Result<ArrayRef> {
    let mut views_buf = Vec::with_capacity(string_view_array.len());
    let mut null_builder = NullBufferBuilder::new(string_view_array.len());

    let start_array = as_int64_array(&args[0])?;

    // In either case of `substr(s, i)` or `substr(s, i, cnt)`
    // If any of input argument is `NULL`, the result is `NULL`
    match args.len() {
        1 => {
            for ((str_opt, raw_view), start_opt) in string_view_array
                .iter()
                .zip(string_view_array.views().iter())
                .zip(start_array.iter())
            {
                if let (Some(str), Some(start)) = (str_opt, start_opt) {
                    let (start, end) = get_true_start_end(str, start, None);
                    let substr = &str[start..end];

                    make_and_append_view(
                        &mut views_buf,
                        &mut null_builder,
                        raw_view,
                        substr,
                        start as u32,
                    );
                } else {
                    null_builder.append_null();
                    views_buf.push(0);
                }
            }
        }
        2 => {
            let count_array = as_int64_array(&args[1])?;
            for (((str_opt, raw_view), start_opt), count_opt) in string_view_array
                .iter()
                .zip(string_view_array.views().iter())
                .zip(start_array.iter())
                .zip(count_array.iter())
            {
                if let (Some(str), Some(start), Some(count)) =
                    (str_opt, start_opt, count_opt)
                {
                    if count < 0 {
                        return exec_err!(
                            "negative substring length not allowed: substr(<str>, {start}, {count})"
                        );
                    } else {
                        let (start, end) =
                            get_true_start_end(str, start, Some(count as u64));
                        let substr = &str[start..end];

                        make_and_append_view(
                            &mut views_buf,
                            &mut null_builder,
                            raw_view,
                            substr,
                            start as u32,
                        );
                    }
                } else {
                    null_builder.append_null();
                    views_buf.push(0);
                }
            }
        }
        other => {
            return exec_err!(
                "substr was called with {other} arguments. It requires 2 or 3."
            )
        }
    }

    let views_buf = ScalarBuffer::from(views_buf);
    let nulls_buf = null_builder.finish();

    // Safety:
    // (1) The blocks of the given views are all provided
    // (2) Each of the range `view.offset+start..end` of view in views_buf is within
    // the bounds of each of the blocks
    unsafe {
        let array = StringViewArray::new_unchecked(
            views_buf,
            string_view_array.data_buffers().to_vec(),
            nulls_buf,
        );
        Ok(Arc::new(array) as ArrayRef)
    }
}

fn string_substr<'a, V, T>(string_array: V, args: &[ArrayRef]) -> Result<ArrayRef>
where
    V: ArrayAccessor<Item = &'a str>,
    T: OffsetSizeTrait,
{
    match args.len() {
        1 => {
            let iter = ArrayIter::new(string_array);
            let start_array = as_int64_array(&args[0])?;

            let result = iter
                .zip(start_array.iter())
                .map(|(string, start)| match (string, start) {
                    (Some(string), Some(start)) => {
                        if start <= 0 {
                            Some(string.to_string())
                        } else {
                            Some(string.chars().skip(start as usize - 1).collect())
                        }
                    }
                    _ => None,
                })
                .collect::<GenericStringArray<T>>();
            Ok(Arc::new(result) as ArrayRef)
        }
        2 => {
            let iter = ArrayIter::new(string_array);
            let start_array = as_int64_array(&args[0])?;
            let count_array = as_int64_array(&args[1])?;

            let result = iter
                .zip(start_array.iter())
                .zip(count_array.iter())
                .map(|((string, start), count)| {
                    match (string, start, count) {
                        (Some(string), Some(start), Some(count)) => {
                            if count < 0 {
                                exec_err!(
                                "negative substring length not allowed: substr(<str>, {start}, {count})"
                            )
                            } else {
                                let skip = max(0, start.checked_sub(1).ok_or_else(
                                    || exec_datafusion_err!("negative overflow when calculating skip value")
                                )?);
                                let count = max(0, count + (if start < 1 { start - 1 } else { 0 }));
                                Ok(Some(string.chars().skip(skip as usize).take(count as usize).collect::<String>()))
                            }
                        }
                        _ => Ok(None),
                    }
                })
                .collect::<Result<GenericStringArray<T>>>()?;

            Ok(Arc::new(result) as ArrayRef)
        }
        other => {
            exec_err!("substr was called with {other} arguments. It requires 2 or 3.")
        }
    }
}

#[cfg(test)]
mod tests {
    use arrow::array::{Array, StringArray, StringViewArray};
    use arrow::datatypes::DataType::{Utf8, Utf8View};

    use datafusion_common::{exec_err, Result, ScalarValue};
    use datafusion_expr::{ColumnarValue, ScalarUDFImpl};

    use crate::unicode::substr::SubstrFunc;
    use crate::utils::test::test_function;

    #[test]
    fn test_functions() -> Result<()> {
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::Utf8View(None)),
                ColumnarValue::Scalar(ScalarValue::from(1i64)),
            ],
            Ok(None),
            &str,
            Utf8View,
            StringViewArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::Utf8View(Some(String::from(
                    "alphabet"
                )))),
                ColumnarValue::Scalar(ScalarValue::from(0i64)),
            ],
            Ok(Some("alphabet")),
            &str,
            Utf8View,
            StringViewArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::Utf8View(Some(String::from(
                    "this és longer than 12B"
                )))),
                ColumnarValue::Scalar(ScalarValue::from(5i64)),
                ColumnarValue::Scalar(ScalarValue::from(2i64)),
            ],
            Ok(Some(" é")),
            &str,
            Utf8View,
            StringViewArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::Utf8View(Some(String::from(
                    "this is longer than 12B"
                )))),
                ColumnarValue::Scalar(ScalarValue::from(5i64)),
            ],
            Ok(Some(" is longer than 12B")),
            &str,
            Utf8View,
            StringViewArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::Utf8View(Some(String::from(
                    "joséésoj"
                )))),
                ColumnarValue::Scalar(ScalarValue::from(5i64)),
            ],
            Ok(Some("ésoj")),
            &str,
            Utf8View,
            StringViewArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::Utf8View(Some(String::from(
                    "alphabet"
                )))),
                ColumnarValue::Scalar(ScalarValue::from(3i64)),
                ColumnarValue::Scalar(ScalarValue::from(2i64)),
            ],
            Ok(Some("ph")),
            &str,
            Utf8View,
            StringViewArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::Utf8View(Some(String::from(
                    "alphabet"
                )))),
                ColumnarValue::Scalar(ScalarValue::from(3i64)),
                ColumnarValue::Scalar(ScalarValue::from(20i64)),
            ],
            Ok(Some("phabet")),
            &str,
            Utf8View,
            StringViewArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("alphabet")),
                ColumnarValue::Scalar(ScalarValue::from(0i64)),
            ],
            Ok(Some("alphabet")),
            &str,
            Utf8,
            StringArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("joséésoj")),
                ColumnarValue::Scalar(ScalarValue::from(5i64)),
            ],
            Ok(Some("ésoj")),
            &str,
            Utf8,
            StringArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("joséésoj")),
                ColumnarValue::Scalar(ScalarValue::from(-5i64)),
            ],
            Ok(Some("joséésoj")),
            &str,
            Utf8,
            StringArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("alphabet")),
                ColumnarValue::Scalar(ScalarValue::from(1i64)),
            ],
            Ok(Some("alphabet")),
            &str,
            Utf8,
            StringArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("alphabet")),
                ColumnarValue::Scalar(ScalarValue::from(2i64)),
            ],
            Ok(Some("lphabet")),
            &str,
            Utf8,
            StringArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("alphabet")),
                ColumnarValue::Scalar(ScalarValue::from(3i64)),
            ],
            Ok(Some("phabet")),
            &str,
            Utf8,
            StringArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("alphabet")),
                ColumnarValue::Scalar(ScalarValue::from(-3i64)),
            ],
            Ok(Some("alphabet")),
            &str,
            Utf8,
            StringArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("alphabet")),
                ColumnarValue::Scalar(ScalarValue::from(30i64)),
            ],
            Ok(Some("")),
            &str,
            Utf8,
            StringArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("alphabet")),
                ColumnarValue::Scalar(ScalarValue::Int64(None)),
            ],
            Ok(None),
            &str,
            Utf8,
            StringArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("alphabet")),
                ColumnarValue::Scalar(ScalarValue::from(3i64)),
                ColumnarValue::Scalar(ScalarValue::from(2i64)),
            ],
            Ok(Some("ph")),
            &str,
            Utf8,
            StringArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("alphabet")),
                ColumnarValue::Scalar(ScalarValue::from(3i64)),
                ColumnarValue::Scalar(ScalarValue::from(20i64)),
            ],
            Ok(Some("phabet")),
            &str,
            Utf8,
            StringArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("alphabet")),
                ColumnarValue::Scalar(ScalarValue::from(0i64)),
                ColumnarValue::Scalar(ScalarValue::from(5i64)),
            ],
            Ok(Some("alph")),
            &str,
            Utf8,
            StringArray
        );
        // starting from 5 (10 + -5)
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("alphabet")),
                ColumnarValue::Scalar(ScalarValue::from(-5i64)),
                ColumnarValue::Scalar(ScalarValue::from(10i64)),
            ],
            Ok(Some("alph")),
            &str,
            Utf8,
            StringArray
        );
        // starting from -1 (4 + -5)
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("alphabet")),
                ColumnarValue::Scalar(ScalarValue::from(-5i64)),
                ColumnarValue::Scalar(ScalarValue::from(4i64)),
            ],
            Ok(Some("")),
            &str,
            Utf8,
            StringArray
        );
        // starting from 0 (5 + -5)
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("alphabet")),
                ColumnarValue::Scalar(ScalarValue::from(-5i64)),
                ColumnarValue::Scalar(ScalarValue::from(5i64)),
            ],
            Ok(Some("")),
            &str,
            Utf8,
            StringArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("alphabet")),
                ColumnarValue::Scalar(ScalarValue::Int64(None)),
                ColumnarValue::Scalar(ScalarValue::from(20i64)),
            ],
            Ok(None),
            &str,
            Utf8,
            StringArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("alphabet")),
                ColumnarValue::Scalar(ScalarValue::from(3i64)),
                ColumnarValue::Scalar(ScalarValue::Int64(None)),
            ],
            Ok(None),
            &str,
            Utf8,
            StringArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("alphabet")),
                ColumnarValue::Scalar(ScalarValue::from(1i64)),
                ColumnarValue::Scalar(ScalarValue::from(-1i64)),
            ],
            exec_err!("negative substring length not allowed: substr(<str>, 1, -1)"),
            &str,
            Utf8,
            StringArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("joséésoj")),
                ColumnarValue::Scalar(ScalarValue::from(5i64)),
                ColumnarValue::Scalar(ScalarValue::from(2i64)),
            ],
            Ok(Some("és")),
            &str,
            Utf8,
            StringArray
        );
        #[cfg(not(feature = "unicode_expressions"))]
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("alphabet")),
                ColumnarValue::Scalar(ScalarValue::from(0i64)),
            ],
            internal_err!(
                "function substr requires compilation with feature flag: unicode_expressions."
            ),
            &str,
            Utf8,
            StringArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("abc")),
                ColumnarValue::Scalar(ScalarValue::from(-9223372036854775808i64)),
            ],
            Ok(Some("abc")),
            &str,
            Utf8,
            StringArray
        );
        test_function!(
            SubstrFunc::new(),
            &[
                ColumnarValue::Scalar(ScalarValue::from("overflow")),
                ColumnarValue::Scalar(ScalarValue::from(-9223372036854775808i64)),
                ColumnarValue::Scalar(ScalarValue::from(1i64)),
            ],
            exec_err!("negative overflow when calculating skip value"),
            &str,
            Utf8,
            StringArray
        );

        Ok(())
    }
}
datafusion_functions/unicode/substr.rs

datafusion_functions/unicode/
substr.rs
